1. Field of the Invention
The present invention relates to a linear motion rolling guide unit suitably applied for machine tools, industrial robots, precision processing equipment and testing equipment, in which sliders slide on track rails with a number of rolling elements interposed therebetween.
2. Description of the Prior Art
Linear motion rolling guide units generally have sliders mounted astride track rails with a large number of rolling elements interposed therebetween so that the sliders can slide on the track rails. The sliders can be guided forwardly and backwardly with high precision over relatively long distances. One such conventional linear motion rolling guide unit is shown in FIGS. 9 and 10.
The linear motion rolling guide unit shown in FIG. 9 includes a track rail 2 and a slider 1 straddling the track rail 2 in such a way that it can move relative to or slide on the track rail 2. The track rail 2 has raceway surfaces 5 formed in raceway grooves on longitudinally extending side wall surfaces 21 thereof. The slider 1 is slidably mounted astride the track rail 2. The slider 1 includes: a casing 3 having raceway surfaces 9 formed in raceway grooves at positions facing the raceway surfaces 5 on the track rail 2; a number of rolling elements 7 trapped between the facing raceway surfaces 5 and 9 to allow relative motion between the rail and the casing; ball retaining bands 18 enclosing the rolling elements 7 to prevent them from coming off the casing 3; under seals 8 to seal a gap between the track rail 2 and the casing 3; and end caps 6 attached to the longitudinal ends of the casing 3, the longitudinal direction being the direction in which the casing slides.
The casing 3 has its underside recessed to form a rail accommodating recess 10. Similarly, the end caps 6 are also formed with a recessed groove 12 (see FIG. 10) that straddles and accepts the track rail 2. The end caps 6 are each provided with an end seal 17 that provides sealing between the rail 2 and the slider 1. The end caps 6 also have a grease nipple 22 for supplying lubricant to the sliding surfaces between the rail 2 and the slider 1. The end caps 6 are also formed, on each side, with raceway grooves 13 and direction changing passages 11. The raceway grooves 13 cooperate with the track rail 2 to form raceways through which the rolling elements 7 move. The direction changing passages 11 in the end caps cause the rolling elements 7 to change their direction for circulation.
This linear motion rolling guide unit is constructed as described above, with the slider 1 mounted astride the track rail 2 and with the rolling elements 7 trapped between the track rail 2 and the slider 1 to allow the slider 1 to freely slide on the track rail 2. The rolling elements 7, which run loaded along the raceway surfaces 5 on the track rail 2, are led into the direction changing passages 11 formed in the end caps 6 and from there into return passages 14 formed in the upper part of the casing 3 parallel to the raceway surfaces 9, thus endlessly circulating through the endless circulation path. In this way, with the loaded rolling elements 7 trapped and running between the raceway surfaces 9 formed in the casing 3 and the raceway surfaces 5 on the track rail 2, the slider 1 and the track rail 2 can slidably move relative to each other. Radial loads and moment loads acting through the slider 1 in vertical and horizontal directions are born by the track rail 2.
The linear motion rolling guide unit shown in FIGS. 9 and 10 is generally used in an assembled condition shown in FIG. 11. That is, two parallel track rails 2, 2 are fixedly installed on a base 20; two or more sliders I are mounted astride each of the track rails 2, 2; a slide table 4 is secured to the sliders 1; then equipment put on the slide table 4 is moved back and forth in the direction of arrow G.
A means to secure the slide table 4 to the sliders 1 is constructed as follows. The upper surface of the casing 3 of the slider 1 is formed with four threaded holes 15 and the slide table 4 has bolt insertion holes 16 made in positions corresponding to the threaded holes 15. With the slide table 4 placed on the sliders 1, bolts are inserted through the bolt insertion holes 16 and then tightened to fix the slide table 4 to the sliders 1.
Instead of the slide table 4 with the planar upper surface as shown in FIG. 11, a slide table 24 with the upper surface formed with dovetail grooves 23 as shown in FIG. 12 may be used. Like the slide table 4 with the flat upper surface, the slide table 24 with the dovetail grooves is formed with bolt insertion holes (not shown) at positions corresponding to the threaded holes 15 in the casing 3 and is secured to the slider 1 in the similar manner.
With the conventional fixing means described above, however, the bolt insertion holes 16 formed in the slide table 4 must be aligned perfectly with the four threaded holes 15 formed in the casing 3 of the slider 1. Where two or more types of slide tables 4 are to be used interchangeably, each of the slide tables must have bolt insertion holes made in precisely the same positions. Conversely, to allow one kind of slide table 4 to be secured to various kinds of linear motion rolling guide units of different sizes requires that the threaded holes 15 be formed at the same positions irrespective of the sizes of the casings 3. These problems stem from the fact that the fixing means for the casings 3 and the slide table 4 has little degree of freedom. It is therefore an important task to increase the level of freedom of the fixing means.
In mounting a work on the slide table, a general procedure involves putting the dovetail-grooved slide table 24 on the casings 3 and fixing them together and then securing the work to the dovetail grooves 23 in the slide table 24. This increases the overall cross-sectional height due to the slide table 24 interposed, failing to meet the demand for lowering the overall height.